1. Field of the Invention
The present invention relates to a solid-state imaging device and a method of manufacturing the same. The present invention also relates to an electronic apparatus using such a solid-state imaging device and a method of manufacturing the same.
2. Description of the Related Art
Image sensors are provided for devices applicable to various fields including cameras and video cameras.
The image sensor for any of such devices includes a number of pixels. The efficiency of the device as a whole depends on the dimensions of the pixel and also the configuration thereof.
A device for color images includes different types of pixels, red, green, and blue, which are typically provided with absorption color filter materials in solid state originated from organic materials.
For improving the efficiency in the pixel, a lens with a size corresponding to the pixel is typically used to keep incident light to be focused on a light-receiving element of the pixel to allow the pixel to receive the light incident thereon as much as possible, preventing the light from dispersing to surrounding pixels.
However, there may be a limit on using such a simplified lens with pixel size. The more the angle of incident light increases, the more difficult for the incident light to be retained in the pixel because of reaching to the limit. In other words, there is a limit to an angle of oblique incident light which can be corrected by the lens, and therefore if the aspect ratio of the pixel, the value obtained by dividing the width of the pixel by the height thereof, is small, the influence thereof may increase.
Therefore, since the pixel size has been reduced recently, it is more difficult for the pixel to control the influence of such color mixture using a standard on-chip lens technology. Besides, since color filters for the respective pixels may be needed, which are typically made of materials originated from organic resist, a height of the device may further increase. Thus, the existence of these color filters reduces the aspect ratio, causing color mixture to be obvious. Particularly, the smaller the pixel size is, the more the color mixture becomes obvious.
In addition, if the pixel size is reduced to 1 μm in width, the lens size may have a value close to the wavelength of light passing through the lens and gradually stops acting as a lens. In other words, the lens may stop collecting the light passing through the lens. Thus, any advantageous effect can hardly be found in the configuration of device based on the related-art lens, if the pixel size is small. Therefore, a newly devised system may be required for retaining light in pixels.
Several investigators have proposed the use of “artificial” lenses, such as a Fresnel lens, a diffraction optics lens, and a digital lens, to introduce rays of light into a pixel even when any standard lens hardly yields sufficient results (see, for example, Japanese Unexamined Patent Application Publication No. 2006-74055, and Japanese Unexamined Patent Application Publication No. 2006-351972).
Such a structure is useful in introduction of light correctly, compared with a lens typically used in the art, but having some disadvantages, such as an increase in wavelength dependency and complexity in manufacturing process.
It should be noted that a small-sized pixel may cause a still larger problem. That is, the aforementioned design requires a physical space for the action of the pixel, or requiring an extremely large width of the pixel. Thus, it is not practical to apply the aforementioned design to the small-sized pixel. The lens may be larger than the pixel. The size limit of lens depends on the wavelength of incident light, so that it can be the fundamental limit in most cases.